1 Field of the Invention
This invention relates to a process of transporting, e.g., in a conduit, a water slurry containing comminuted solids.
2. Description of the Prior Art
The transportation of solid particles through pipelines has become an economically attractive method of moving bulk solids over long distances. This method has proven effective for transporting coal, sulfur, wax and other solids capable of being converted into particulate form. The solid material is generally comminuted by pulverization, shearing or other means of degradation, suspended in a liquid carrier medium, and then injected under pressure into a conduit, e.g., a pipeline. If the density of the comminuted matter is significantly greater than the supporting liquid carrier, the particles tend to settle to the bottom of the pipeline, especially where obstructions interfere with the flow of the slurry or in low spots in the line. This problem is particularly pronounced during shut-down of flow through the pipeline or when the comminuted matter is subject to agglomeration. Settling of the solid particles can result in plugging, pump blockages and substantial pressure gradients within the pipeline. It is possible to approximate a homogeneous liquid-solid slurry by maintaining the slurry flow under turbulent flow conditions (e.g., at a Reynolds number greater than about 4,000)--but high pumping costs necessarily result.
U.S. Pat. No. 3,432,209 to Scott teaches reducing the settling rate of inorganic salts in a petroleum-inorganic salt slurry by adding to the slurry an anionic sulfonate dispersant. The dispersant attaches to the salt granules, thereby lowering the density of the complex.
U.S. Pat. No. 3,264,038 to Shock et al. teaches protecting a solid from a carrier liquid by coating the solid with a material which is insoluble in and unreactive with the carrier liquid.
U.S. Pat. No. 3,359,040 to Every et al. teaches adsorbing water onto the surface of a solid pulverant material and then mixing the solid with a hydrocarbon carrier.
U.S. Pat. No. 3,637,263 to Wasp teaches transporting a water-coal slurry by incorporating in the slurry an inorganic finely divided water insoluble solid carrier having a specific gravity greater than 1.6.
U.S. Pat. No. 3,389,714 to Hughes teaches increasing the pumpability of viscous liquids and liquid-solid slurries by adding a fluid to the liquid, and maintaining the liquid under sufficient temperature and pressure to keep the fluid in a gaseous state. The gaseous fluid is adsorbed in the liquid thereby reducing its viscosity.
Other prior art references have proposed methods for reducing the tendency of some types of particles to form agglomerations within liquid-solid slurry systems. For example, U.S. Pat. No. 3,269,401 to Scott et al. teaches facilitating the flow of wax-bearing oil through pipelines by dissolving in the oil at superatmospheric pressure and above the oil's pour point, a gas which can be nitrogen, carbon dioxide, flue gas, hydrocarbons having less than three carbon atoms and mixtures thereof. Upon shut-down of the pipeline flow, the pressure is lowered in the pipeline to below the bubble point, thereby causing gas to separate from the oil as small bubbles. These bubbles become associated with the existing and newly formed wax crystals, and prevent the formation of a strong wax structure.
U.S. Pat. No. 3,292,647 to Scott teaches subjecting a wax-containing oil, at a temperature below the pour point of the wax, to shearing forces sufficient to break down the wax structure into a fine dispersion, and injecting a gas into the oil to prevent regrowth of the wax crystals.
None of the prior art references, however, teach a means of lowering the effective density of porous solids in a liquid-solids slurry.